1. Field of the Invention
The present invention relates to drive mandrels or shafts for gripping the internal surfaces of sleeves or tubes on which web material may be wound.
In the winding and rewinding of web material such as paper, cloth and other sheet material, the web is wound on a sleeve or tube having an inside diameter slightly larger than the shaft on the winding mechanism. In this manner the sleeve may readily be slipped on and off the shaft. As a result an arrangement must be provided to effect a secure driving connection between the shaft and sleeve upon which the web material is wound. Accordingly there exists shafts that are expandable to grip against the web sleeve to provide a secure driving engagement.
The present invention is directed to such expandable shafts and the method of making them that provides functional and structural advantages over present expandable shafts.
2. Description of the Prior Art
Expandable shafts or mandrels are generally constructed with elements on the surface adapted to be extended radially outward by inflation of bladders within the shaft. Shaft designs fall into two general categories, the lug type and slotted rail type. The former contemplates a number of discreet lugs located at different points along the shaft. Customarily there is one or more bladders located within the shaft that are appropriately inflated to cause the lugs to extend radially outward to grip the web sleeve that surrounds the shaft. The slotted type of expandable shaft customarily includes a plurality of equally spaced slots around the circumference of the shaft and elongated pressure elements located within the slots. Individual bladders located within the shaft slots are inflated to bear against the pressure elements and extend them radially outward for the gripping of a surrounding web sleeve.
Examples of these prior art shafts are shown in U.S. Pat. Nos. 3,493,189; 3,552,672; 3,904,144 and 4,473,195.
These expandable shafts of the prior art are customarily made of aluminum extrusions or machined steel cylinder bodies having steel end journals. The machined steel cylinder bodies are used to support the larger weight and the higher stiffness applications. The weight of these steel expandable shafts is often excessive and frequently outside the current OSHA weight limits for lifting by individuals without mechanical assistance. The aluminum shafts on the other hand, are limited to lighter weights and less stiffness dependent applications. These are some of the disadvantages of prior art expandable shafts that the present design serves to overcome.